Oil well pumps are well known in the industry and generally are located at the lower portion of well tubing which serves as a passage for pump fluid. Essentially, such pumps include a barrel through which a plunger is reciprocated by an appropriate rod extending upwardly through the well tubing to an appropriate driver at ground level. The plunger is provided with a one-way check valve which passes fluid to be pumped into the plunger on its down stroke and closes on the up stroke so that the fluid is lifted through the tubing to the surface.
A special problem with such pumps resides in proper lubrication for movement of the plunger within the pump barrel. Various types of seals have been provided between the plunger and inside wall of the barrel in an effort to keep out sand or grit from between the outside wall of the plunger and inside wall of the barrel itself which sand or grit can damage the pump and result in the necessity of frequent replacement.
An example of a solution to the proposed problem is set forth in U.S. Pat. No. 3,773,441 issued Nov. 20, 1973 and entitled COMBINED SAND BAILER AND FLUID PUMP WITH AUTOMATIC GRIT SEPARATOR AND LUBRICATOR. The pump and bailer described in this patent provides a fluid reservoir communicating through a filter with oil being pumped. This reservoir is in the form of an annular chamber about the plunger between the inside walls of the barrel and exterior walls of the plunger between appropriate upper and lower seals. Essentially, part of the oil being pumped is bypassed through the filter into the reservoir wherein the same serves as a lubricant for movement of the plunger and is maintained free of grit, sand and the like by the filter arrangement.
The basic concept of providing an annular fluid reservoir filled with oil or fluid as a lubricating medium has solved the problem of frequent pump replacement. On the other hand, the manufacturing cost and maintenance of the pump itself is somewhat increased, replacement of the filter being required periodically. There still appears to be room for improvement in a combined pump and bailer which can function for long periods without abrasion by grit and sand working to the area between the plunger and barrel walls wherein relative reciprocating movement takes place.